The present invention is related to a variable lightwave functional circuit and a variable lightwave functional apparatus. More specifically, the present invention is directed to a variable lightwave functional circuit and a variable lightwave functional apparatus, using a mode coupling within a polarization-maintaining optical fiber.
Network technology of optical fiber communication systems has been conducted in practical fields in connection with appearances of optical fiber amplifiers in a front half decade in 1990, and is being rapidly developed. In the present stage, there are certain possibilities that ultra-long distance (e.g., up to 10,000 Km) and very high speed (e.g., up to 40 Gb/s) wavelength division multiplexed transmission systems (WDM system operable up to, e.g., 64 wavelengths) could be realized. Then, optical fiber information communication networks may be conceivable as the most important infrastructure in the beginning stage of 21 century. However, up to now, while optical fiber communication systems are mainly employed only in point-to-point correspondence trunk line systems, conventional coaxial cables and semiconductor integrated circuits/electronic devices may constitute major basic elements in network portions. Since the Internet has been currently developed in explosive manners, extensions of transfer capacities which are required for future's networks could be predicted by that the transfer capacities are extended twice per 12 months. This extension rate of the transfer capacities exceeds a so-called “Moore's law (twice per 18 months)” related to semiconductor integrated circuits. Soon or later, there is no doubt about such a fact that WDM optical networks using light are necessarily required also in these network portions. However, under the present situation, optical devices employed in such WDM optical networks have not yet been well-developed, so that very rapid development of these optical devices is necessarily needed.